a) Field of the Invention
The invention is directed to a radiation-transparent die half for a forming die in which a beam outlet from a forming beam outlet surface is spatially limited by a diaphragm.
b) Description of the Related Art
There are known forming techniques for the production of contact lenses which lead to a fully formed lens without the need for subsequent machining of surfaces and edges. The forming dies that are used comprise specially shaped female and male die elements, the contact lenses being shaped from a cross-linkable starting material in the open cavity of these die elements.
When the cross-linking is initiated by radiation energy, particularly by irradiation with UV light, it is known from EP 0 637 490 B1 to use UV-transparent material, preferably quartz in particular also because of its hardness and durability through which the irradiation with UV light is carried out with energy applied to one side, e.g., for the male die part.
A diaphragm is used for spatially limiting the initiating radiation on the lens material located in the cavity, so that the edge of the lens is shaped exclusively by spatial beam limiting. For producing the diaphragm, it is suggested that a thin layer of chrome is preferably applied, e.g., to the forming surface of the male die element, by lithographic processes.
A disadvantage consists in the high susceptibility of the thin layer of chrome to mechanical or other environmental influences which destroy the diaphragm function. In EP 0 637 490 B1, contact between the two die halves is prevented during the forming process or a protective coating is provided for the diaphragm in order to protect the forming surface and/or the diaphragm located thereon from mechanical influences as far as possible; however, should damage occur at the thin chrome layer, this damage can not be eliminated and the die must be replaced.
A further disadvantage consists in the technical and financial expenditure required for producing the chrome layer which is a result particularly of the applied lithographic fabrication process. The process is applied primarily to molds which are symmetric with respect to rotation. In the absence of rotational symmetry, e.g., in the case of non-symmetric forming surfaces with respect to rotation, centering of the forming mask is critical or requires unreasonably high expenditure.
Aside from the construction mentioned above, WO 03/035376 A1 discloses another suggestion which provides a relatively costly design for a holder to hold a radiation-transparent die element for the purpose of spatial beam limiting. A separate holder part which encloses the radiation-transparent die element cooperates with another annular diaphragm which is held mechanically in the holder and which has a conically tapering inner diameter.